Seminars 2013



  • Tuesday 22 January 2013 at 10.15 in A315: Johan Bijnens (Lund)
    Hadronic Light-by-Light for the Muon Anomalous Magnetic Moment
    Abstract: I will give a short overview of the theory behind the muon anomalous magnetic moment in the Standard Model with an emphasis on the hadronic light-by-light contribution.
  • 4-8 March 2013 in E204: HoloGrav 2013 Workshop Helsinki
    Program is here
  • Thursday 28 March 2013 at 10.15 in A315: Patta Yogendran (IISER Mohali, Punjab, India)
    Holographic Superfluids reprised
    Abstract: We will discuss a few elementary questions about superfluids which seem worth investigating in the holographic context.
  • Wednesday 3 April 2013 at 14.00 in D101: Paul Hoyer (Helsinki) Special seminar, note time and place!
    Forty-five fascinating years of physics
  • Tuesday 9 April 2013 at 10.15 in A315: Hannu Kurki-Suonio (Helsinki)
    Planck results
    Abstract: New Planck satellite measurements of cosmic background radiation are discussed: how they were obtained, what their implications are and what now follows.
  • Tuesday 23 April 2013 at 10.15 in A315: Arttu Rajantie (Imperial College)
    Magnetic monopoles in the cosmos and at the LHC
    Abstract: Magnetic monopoles are hypothetical particles with non-zero magnetic charge. Their existence is predicted by string theory and grand unified theories, and if the temperature of the universe ever exceeded their mass, they should have been produced in large numbers. Yet, they have not been found in spite of extensive searches. I give a review of the theoretical and experimental status of magnetic monopoles, including the new MoEDAL experiment at the LHC. I also discuss theoretical problems in the calculation of their production rate in particle collisions.
  • Tuesday 7 May 2013 at 10.15 in A315: Kirtiman Ghosh (University of Oklahoma, Still Water, USA)
    Top-jets as a probe of constrained minimal supersymmetric standard model with degenerate top squark and lightest supersymmetric particle
    Abstract: The degenerate stop NLSP and neutralino LSP scenario is well motivated but hard to detect at the collider experiments. We propose a novel signature for detection of this scenario at the Large Hadron Collider and demonstrate its feasibility. In cMSSM with stop-NLSP, gluinos are in general much heavier than the lighter stop and thus, it decays dominantly to high transverse momentum (p_T) top-stop pairs. We consider gluino pair production and study two high p_T top jets and missing energy as the signature of this scenario.
  • Tuesday 14 May 2013 at 10.15 in A315: Laura Bethke (Imperial College)
    Anisotropic Gravitational Wave Background from Massless Preheating
    Abstract: Gravitational waves (GWs) are an exciting phenomenon in Cosmology. Although they are hard to detect, GWs from different sources have different spectral signatures and can travel freely to us from their emission until today, providing a new wealth of information about the early Universe. In this talk I will describe how massless preheating after inflation leads to a strongly anisotropic GW background, even on large angular scales. This effect is caused by the presence of a light scalar field and could therefore be expected in many different models. If future experiments are able to observe the GW background from preheating, these anisotropies could provide a way to distinguish different models of preheating and inflation.
  • Tuesday 21 May 2013 at 10.15 in A315: Simon Caron-Huot (NBI, CPH)
    When does the gluon reggeize
    Abstract: I will discuss a novel class of Wilson line operators that are supported on a natural ‘completion’ of light cones. By a simple conformal transformation, these operators are shown to govern the high-energy limit of scattering amplitudes (Regge limit), in any CFT or near-CFT such as QCD in the ultraviolet, and their anomalous dimension is the BFKL kernel. In the talk I’ll use these operators to answer some basic questions regarding the structure of the Regge limit — for example, when do gluon-exchange amplitudes exhibit pure power-law energy dependence (Regge pole behavior)?
  • Thursday 23 May 2013 at 10.15 in A315: Daniel Litim (Sussex)
    Pulling oneself over the fence: a bootstrap for quantum gravity
    Abstract: Asymptotic freedom is a key ingredient in the successful construction of the Standard Model. It has been conjectured long ago that metric quantum gravity may as well fit into the picture – despite its notorious perturbative non-renormalisability – provided that the theory turns out to be asymptotically safe. We recall the underlying ideas and challenges, and contrast asymptotic freedom with asymptotic safety. We also propose a self-consistent search strategy for the latter and show new results for a simplified version of quantum gravity. Implications for the asymptotic safety conjecture are discussed.
  • Tuesday 28 May 2013 at 10.15 in A315: Mario Schröck (Graz)
    The effects of Dirac low-mode truncation on the hadron mass spectrum in lattice QCD
    Abstract: Chiral symmetry breaking in Quantum Chromodynamics is associated with the low lying spectral modes of the Dirac operator according to the Banks-Casher relation. We investigate how removal of a variable number of low lying modes from the valence quark sector affects the masses of the ground states and first excited states of baryons and mesons in two flavor lattice QCD.
  • Wednesday 29 May 2013 at 10.15 in A315 (Note day!): Owe Philipsen (Frankfurt)
    Finite density QCD from an effective lattice theory
    Abstract: QCD at finite baryon density is not amenable to Monte Carlo simulations because of the notorious Sign Problem. Apprxomiate methods to circumvent it have been developed but are restricted to small chemical potentials. Recently a new strategy utilising an effective theory has been presented, which is derived analytically from lattice QCD by combined strong coupling and hopping expansions. So far the effective theory is valid for heavy quarks only. However, its sign problem is mild and can be solved by complex Langevin methods. The deconfinement transition can be computed for all chemical potentials. Moreover, for the first time the transition to cold nuclear matter has been calculated from QCD directly.
  • Monday 3 June 2013 at 14.15 in A315 (note time!): Georg Bergner (Frankfurt)
    Supersymmetry on the lattice and simulations of N=1 supersymmetric Yang-Mills theory
    Abstract: The numerical simulation of supersymmetric theories on the lattice is still challenging subject of recent investigations. I will provide a short summary of approaches towards a general solution for the realization of supersymmetry on the lattice. In N=1 supersymmetric Yang-Mills theory, the gauge part of supersymmetric extensions of the standard model, supersymmetry can be restored in the continuum limit according to theoretical predictions. However, there are technical challenges for the simulations and the measurements of the states in this model. In this talk I will provide a status report on the current results concerning the mass spectrum of this theory.
  • Tuesday 4 June – Friday 7 June 2013 : Talks of the HIP workshop Cosmological perturbations post-Planck
  • Monday 10 June 2013 at 14.15 in A315: Jouni Niskanen (Helsinki) Special seminar!
    Niskanen’s cat
  • Tuesday 6 August 2013 at 10.15 in A315: Jacob Bekenstein (Jerusalem)
    Black hole thermodynamics – then and now
    Abstract: Black hole thermodynamics was developed about 40 years ago in the wake of deepening the understanding of the black hole phenomenon. It has remained lively by ramifying into a few subjects which are active fields of research today. I will describe, from a personal point of view, how the subject started and show how it connects to some contemporary issues in theoretical physics.
  • Tuesday 13 August 2013 at 10.15 in A315: Jarno Rantaharju (Riken AICS, Kobe, Japan)
    The Gradient Flow Coupling in Technicolor Models
    Abstract: Lately, lattice field theory has been used to extensively study technicolor models, a class of candidate models for beyond the Standard Model dynamics. These models should lie close to the lower limit of the conformal window, where the running coupling acquires a nonzero asymptotic value at small energy scales. So far, the most common method for studying the running coupling on the lattice has been the Schrödinger Functional method. I present a study using a novel, Gradient Flow coupling measurement and compare it to the Schrödinger Functional in one prominent technicolor candidate model, the SU(2) gauge theory coupled to 2 fermions in its adjoint representation.
  • Tuesday 3 September 2013 at 10.15 in A315: Oleg Lebedev (Helsinki)
    The different faces of the Higgs
    Abstract: Last year was marked by an event of fundamental importance, that is, the discovery of the Higgs boson. In this talk, I will argue that the Higgs field enjoys a special status in the Standard Model and its extensions. It may provide us with a unique opportunity to probe the hidden sector. Furthermore, it may hold the key to the mysteries of dark matter and inflation, as well as other puzzles of particle physics.
  • Tuesday 10 September 2013 at 14.15 in A315 (note time!): Sabine Hossenfelder (Nordita, Stockholm)
    News from Quantum Gravity Phenomenology
    Abstract: I will talk about recent developments in the search for experimental signatures for quantum gravitational effects. Some of the topics that I will cover are the prospects of finding Planck scale effects in gamma ray bursts, in neutral Kaon oscillations, or with massive quantum oscillators. I will also comment on the possibility of finding holographic noise and, if time permits, on Bekenstein’s proposed table top experiment.This is not a review talk; it is a hand selected assortment of topics I think are interesting.
  • Wednesday 11 September 2013 at 14.15 in A315: Lingfei Wang (Lancaster, UK)
    A new mechanism for curvature perturbations
    Abstract: I will explain the spectator scenario and show its advantages compared to the curvaton scenario, under the latest Planck constraints. The spectator scenario generates a smaller non-Gaussianity, negligible isocurvature perturbations, and less tuning. It agrees well with the current Planck data in the visible sector inflation setup, as an example. It also explains the CMB dipole asymmetry with a brief fast roll phase. I will close the talk by proposing the CMB power multipoles, as an alternative approach independent of the CMB dipole asymmetry mode
  • Tuesday 17 September 2013 at 10.15 in A315: Aleksi Vuorinen (Helsinki)
    Holographic thermalization at intermediate coupling
    Abstract: I will review some recent progress in the use of holographic methods for the description of equilibration in strongly coupled field theory, having applications to heavy ion physics in mind. In particular, I will explain how supplementing the usual type IIB supergravity action with higher derivative corrections will enable one to proceed beyond the infinite coupling limit of N=4 Super Yang-Mills theory, and how this can be seen to qualitatively change the thermalization properties of the system.
  • Wednesday 18 September 2013 at 10.15 in A315 (note day!): Yoshitaka Kuno (Osaka, Japan)
    Search for Muon to Electron Conversion at J-PARC – the COMET Experiment
    Abstract: Muon to electron conversion in a muonic atom is a process of charged lepton flavor violation (CLFV). It is complementary to a rare muon decay to an electron and a photon both experimentally and theoretically. The COMET experiment aims to search for muon to electron conversion at J-PARC with single-event sensitivity of 3×10^(-17) which is about 10,000 improvement over the current limit. Recently COMET has taken a staged approach. COMET Phase-I as the first phase, aims at a single-event sensitivity of 3×10^(-15) with a portion of the full muon beam line and a dedicated detector in about 10^6 sec. The funding for COMET Phase-I was approved as the Japanese Government supplemental budget in 2012, and the construction has started in 2013. The physics run is expected to start in 2016 or so. The COMET Phase-II will follow immediately. In this talk, I will describe physics motivation of CLFV and COMET Phase-I / Phase-II.
  • Tuesday 1 October 2013 at 10.15 in A315: Gautam Bhattacharyya (Saha Institute of Nuclear Physics, Kolkata, India)
    Geometrical CP violation and nonstandard Higgs decays
    We have constructed for the first time a flavor model, based on the smallest discrete symmetry Delta(27) that implements spontaneous CP violation with a complex phase, of geometric origin, which can reproduce all quark masses and mixing data. We show that its scalar sector has exotic properties that can be tested at the LHC.
  • Friday 11 October 2013 at 10.15 in A315 (Note day!): Aleksi Kurkela (CERN)
    Photon production in quark-gluon plasma
    Abstract: TBA
  • Tuesday 15 October 2013 at 10.15 in A315: Holger Bech Nielsen (Niels Bohr Institute)
    What is so special about the Standard Model? Small representations.
    Now it seems that the Standard Model gets more and more supported without yet convincing signs of new physics, so one may with increased strength ask: Why is just the a priori not so obvious Standard Model being selected by Nature? Don Bennett and I started by asking for a quantity depending on the gauge gruop which would be maximal on the Standard Model Group. We found a quantity which is essentially the ratio of the quadratic Casimir for the adjoint representation relative to the quadratic Casimir for the “smallest” faithful representation. Essentially the same maximization principle seems also to deliver the space-time dimension and the representation for the Higgs field. Taking into account the requirements of no anomalies, it is also very close at least to tell what Weyl field representations one shall find. So approximately the whole Standard Model except the number of families come out from such a really “small representation” principle!
  • Tuesday 22 October 2013 at 10.15 in A315: Tomas Brauner (Helsinki)
    Spontaneous symmetry breaking and Nambu-Goldstone bosons: some news in the old story
    Abstract: The concept of spontaneous symmetry breaking is key to understanding of a vast range of physical phenomena such as superfluidity, ferromagnetism, or the origin of masses of elementary particles. I will provide a brief introduction to this classic topic and then review some recent results: (i) Completed classification and counting of Nambu-Goldstone bosons; (ii) A new class of states protected by symmetry: the massive Nambu-Goldstone bosons. I will conclude by outlining some yet unresolved problems, relevant for applications to a variety of quantum many-body systems.

  • Tuesday 29 October 2013 at 10.15 in A315: Kimmo Tuominen (Helsinki)
    Beyond the Standard Model
    Abstract: The existence of the Higgs mechanism and the associated scalar particle has been firmly established by LHC experiments. While the Standard Model (SM) of elementary particle interactions provides an excellent parametrisation of LHC data, the need for physics beyond SM remains as serious as ever: for example the origin of the weak scale and fermion masses, the dark matter abundance and the matter-antimatter asymmetry remain unexplained. Aspects of these issues are discussed in this talk with concrete and testable model examples.
  • Thursday 31 October 2013 at 10.15 in A315: Chris Kouvaris (CP3, Odense)
    The dark side of Stars
    Abstract: I will talk about how compact stars such as white dwarfs and neutron stars can impose constraints on properties of dark matter models. Dark matter accumulation into neutron stars can change the thermal evolution of the star due to dark matter annihilation taking place inside the star. In the case of asymmetric dark matter, WIMP accumulation might lead under certain conditions to the formation of a black hole that can potentially destroy the star, thus imposing constraints on several models of dark matter.
  • Tuesday 5 November 2013 at 10.15 in A315: Alberto Ramos (Desy)
    The gradient flow and the determination of alpha_s
    Measuring the intensity of the strong force has his inherent problems due to the non-perturbative nature of the interaction. In this talk I will review one of the lattice approaches to the problem of how to measure the intensity of strongly coupled gauge theories and some of its most recent developments. These include the use of the gradient flow, a tool that allows an easy non-perturbative definition of the coupling constant, but with the potential of having other applications beyond the lattice.
  • Tuesday 12 November 2013 at 10.15 in A315: Antonio Racioppi (NICPB, Tallinn)
    Towards Completing the Standard Model
    Abstract: We study the standard model (SM) in its full perturbative validity range between LambdaQCD and the U(1)_Y Landau pole, assuming that a yet unknown gravitational theory in the UV does not introduce additional particle thresholds, as suggested by the tiny cosmological constant and the absence of new stabilizing physics at the EW scale. We find that, due to dimensional transmutation, the SM Higgs potential has a global minimum at 10^26 GeV, invalidating the SM as a phenomenologically acceptable model in this energy range. We show that extending the classically scale invariant SM with one complex singlet scalar S allows us to: (i) stabilize the SM Higgs potential; (ii) induce a scale in the singlet sector via dimensional transmutation that generates the negative SM Higgs mass term via the Higgs portal; (iii) provide a stable CP-odd singlet as the thermal relic dark matter due to CP-conservation of the scalar potential; (iv) provide a degree of freedom that can act as an inflaton in the form of the CP-even singlet. The logarithmic behavior of dimensional transmutation allows one to accommodate the large hierarchy between the electroweak scale and the Landau pole, while understanding the latter requires a new non-perturbative view on the SM.
  • Tuesday 26 November 2013 at 10.15 in A315: Tommi Markkanen (Helsinki)
    Applications of Curved Space Field Theory for Scalar Field Models of Inflation
    Now in the wake of the Planck mission a demand for improving the predictions of standard
    inflationary models has arisen. In this talk I will discuss the inclusion of quantum
    corrections in the equations of motion for a scalar matter field present during inflation,
    in the framework of curved space field theory. Among the key questions will be how to
    perform proper renormalization at the equation of motion level, without referring to an
    effective action. I will also present a quantum slow-roll calculation that incorporates the
    important infrared effects of dynamical space-time and show how a re-summing of diagrams
    cures a potential IR enhancement.
  • Tuesday 10 December 2013 at 10.15 in A315: Juha Jäykkä (Nordita)
    Isospinning hopfions
    The problem of constructing internally rotating solitons of fixed angular frequency omega in the Faddeev-Skyrme model is reformulated as a variational problem for an energy-like functional, called pseudoenergy, which depends parametrically on omega. This problem is solved numerically using a gradient descent method, without imposing any spatial symmetries on the solitons, and the dependence of the solitons’ energy on omega, and on their conserved total isospin J. It is found that, generically, the shape of a soliton is independent of omega, and that its size grows monotonically with omega. A simple elastic rod model of time-dependent hopfions is developed which, despite having only one free parameter, accounts well for most of the numerical results.
  • Tuesday 17 December 2013 at 10.15 in A315: Roshan Foadi (Helsinki)
    Composite Higgs scenarios
    I will review scenarios of Higgs compositeness: the Higgs as a pseudo-Goldstone boson, the dilaton, and the technicolor-Higgs.